I'm looking into finding a preowned 993 or 996. In general, how many miles would you consider to be "too high" for miles on a 911? Do "issues" tend to rear its head at a magic number, say around 100,000 (assuming good maintenance records)? I know there's a million variable and lemon factors, but just overall opinions appreciated.

 

Perhaps one guide is the maximum mileage Porsche will provide Extended Warranty. This is 120,000 miles.
The real issue as you have already alluded to, is what is the Service History and who did the Servicing.
For a first purchase I would say on a 996 be looking at 50-80K max, based on the reports from owners of cars with this level of mileage.
Regards Big Bob

 

But I sure like the looks of the 993 a bit better!